FXUS61 KRNK 051204
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
704 AM EST SAT DEC 5 2009

.SYNOPSIS...
LOW PRESSURE WILL DEVELOP AND MOVE RAPIDLY ALONG THE SOUTHEAST
COAST THIS MORNING...REACHING THE OUTER BANKS OF NORTH CAROLINA
BY THIS AFTERNOON...AND EXITING THE MID ATLANTIC COAST AREA BY
THIS EVENING. COLD HIGH PRESSURE WILL BUILD IN BEHIND THE SYSTEM
FOR OVERNIGHT.

&&

.NEAR TERM /THROUGH TONIGHT/...
MOST SURFACE OBSERVATION ABOVE FREEZING EARLY THIS MORNING WITH ONLY 
PATCH DRIZZLE BEING REPORTED ALONG THE BLUE RIDGE. AS MOISTURE 
CONTINUES TO ADVANCE INTO THE AREA WITH A DISTURBANCE TRACKING ALONG 
THE COAST...WILL SEE TEMPERATURES DROP AS AIR COLUMN COOLS TO THE 
WET BULB. LIGHT RAIN WILL QUICKLY TURN OVER TO SNOW ACROSS THE WEST 
EARLY THIS MORNING. ALONG THE FOOTHILLS...HIGHER ELEVATIONS WILL SEE 
THE CHANGE TO SNOW EARLY THIS MORNING...THEN IN THE LOWER ELEVATIONS 
BY LATE IN THE MORNING. ALONG THE VA/NC BORDER...MILD TEMPERATURES 
SHOULD HOLD OFF SNOW CHANCES UNTIL LATE IN THE AFTERNOON. THE 
PIEDMONT OF CENTRAL VIRGINIA...NORTH OF HIGHWAY 460...SHOULD SEE A 
CHANGE OVER BY THE AFTERNOON. THIS STORM IS PICKING UP SPEED AND 
SHOULD EXIT WITH PRECIPITATION ENDING THIS EVENING.

ACCUMULATIONS TRICKY FOR THE FIRST WIDESPREAD SNOW EVENT OF THE 
SEASON. FIRST...MOISTURE ADVANCING INTO THE AREA WAS A FEW HOURS 
LATE AND THIS HAS HELD TEMPERATURES UP THROUGH THE EARLY MORNING 
HOURS. SECOND...GROUND TEMPERATURES IN THE UPPER 30S TO MID 40S 
ACROSS THE AREA WILL MELT SNOW IN THE ONSET. INTO THE 
AFTERNOON...GROUND TEMPERATURES WILL HAVE COOLED AND SNOWFALL RATES 
WILL PICK UP FOR SNOW TO ACCUMULATE. ROAD SURFACES THROUGH THE DAY 
SHOULD WITH STAND ANY ACCUMULATIONS WITH POSSIBLE SLUSH BY DAYS END. 
FORECAST ACCUMULATIONS CAN BE SEE ON RNK WEBSITE...WITH THE HIGHEST 
AMOUNTS OVER THE ALLEGHANY HIGHLANDS AND SOUTHERN SHENANDOAH VALLEY. 
AS THE STORM TRACKS ALONG THE VA/NC COAST...DYNAMICS AND ISENTROPIC 
LIFT INCREASES OVER RNK NORTH. WITH 4 OR MORE INCHES EXPECTED...HAVE 
UPGRADED ALLEGHANY HIGHLANDS AND SOUTHERN SHENANDOAH VALLEY TO A 
WINTER STORM WARNING INTO THIS EVENING. 

TEMPERATURES ANOTHER TOUGH CALL AS AREAS ALONG AND WEST OF THE BLUE 
RIDGE WILL SEE MAXIMUM TEMPERATURES THIS MORNING. IN THE 
PIEDMONT...MAXIMUM TEMPERATURE MAY BE REACHED BY NOON. WITH 
PRECIPITATION FALLING THROUGH THE AFTERNOON AND COLD AIR FILTERING 
IN...TEMPERATURES WILL REMAIN STEADY AND/OR FALL. THE COLDEST AIR OF 
THE SEASON WILL CONTINUE TO FILTER INTO THE REGION WITH SURFACE HIGH 
PRESSURE OVER THE AREA SUNDAY MORNING. WITH COLD AIR AND SNOW ON THE 
GROUND...TEMPERATURE WILL RADIATE DOWN INTO THE 20S...SOME TEENS 
ACROSS THE MOUNTAINS. WITH TEMPERATURES DROPPING VERY QUICKLY 
SATURDAY EVENING...WATER AND SLUSH ON THE ROADS WILL FREEZE 
OVERNIGHT. BLACK ICE WILL BE A PROBLEM...ESPECIALLY ON SECONDARY 
ROADWAYS.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/...
500 MB HEIGHTS RISE AND SURFACE HIGH PRESSURE BUILDS INTO THE AREA 
ON SUNDAY. THE CENTER OF THE HIGH CROSSES THE FORECAST AREA ON 
SUNDAY NIGHT. WENT WITH COOLER MET GUIDANCE FOR MAXIMUM TEMPERATURES 
ON SUNDAY EXPECTING THERE WILL STILL BE SOME SNOW ON THE GROUND FROM 
THE FOOTHILLS WEST ACROSS THE MOUNTAINS. 

MODELS ARE SHOWING A WEAK SHORT WAVE IN THE NORTHERN STREAM ON 
MONDAY. THIS FEATURE PUSHES A WEAK FRONT INTO THE OHIO VALLEY ON 
MONDAY. AS THE HIGH MOVES OFFSHORE...SOUTHWEST LOW LEVEL FLOW WILL 
START INCREASING THE MOISTURE ACROSS THE AREA. LEFT A LOW CHANCE OF 
UPSLOPE SHOWERS IN THE MOUNTAINS. TOOK A BLEND OF GUIDANCE FOR 
SUNDAY NIGHT AND MONDAY.

A COLDER HIGH MOVES INTO THE AREA ON TUESDAY. SLIGHTLY INCREASES 
PROBABILITY OF PRECIPITATION ON TUESDAY NIGHT BASED ON THE TIMING 
AND LIFT OF THE 00Z GFS ENSEMBLE AND ECMWF WITH THE LARGE SOUTHERN 
STREAM SYSTEM.

&&

.LONG TERM /WEDNESDAY THROUGH FRIDAY/...
LEANED MEDIUM RANGE GRIDS TOWARDS A BLEND OF HPCGUIDE AND ECMWF 00Z. 
QUASI ZONAL FLOW EXPECTED WITH SOME AMPLIFICATION OF THE PATTERN ON 
TUESDAY INTO WEDNESDAY. HIGH PRESSURE WILL SLIDE EASTWARD ON 
TUESDAY. DECIDED TO DECREASE POPS FOR TUESDAY AND PLAY BEST CHANCES 
IN THE WEST. MOISTURE SLOWLY INCREASES AS A FRONTAL BOUNDARY 
APPROACHES FROM THE WEST TUESDAY AFTERNOON. AS THE LOW PRESSURE 
CENTER AND FRONT SPREAD EAST THE CHANCES OF PCPN INCREASE TUESDAY 
NIGHT AND WEDNESDAY. ELECTED TO GO WITH LIKELY POPS FOR WEDNESDAY
WITH THE CONSISTENCY OF THE MODELS. AS LOW PRESSURE LIFTS NORTHEAST 
AND COLD FRONT PUSHES INTO THE ATLANTIC OCEAN. KEEP SOME CHCY POPS 
IN THE WESTERN MOUNTAINS WEDNESDAY NIGHT INTO THURSDAY. PLAYED 
HIGHEST POPS IN THE NORTHWEST. HIGH PRESSURE WILL BUILD EAST INTO 
THE AREA FROM THE TENNESSEE VALLEY ON THURSDAY INTO THURSDAY NIGHT.
KEPT SOME CHCY POPS IN THE WEST WITH THE PASSAGE OF A WARM FRONT 
ON FRIDAY.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
IFR TO LIFR CEILINGS AND VISIBILITIES ARE EXPECTED TODAY WITH
WIDESPREAD RAIN AND SNOW. A LOW PRESSURE SYSTEM OFF THE
SOUTH CAROLINA COAST WILL MOVE NORTHEAST TODAY AND TONIGHT. THE
PRECIPITATION WILL BE MAINLY ALL SNOW AT BLF AND LWB. THE
PRECIPITATION WILL BE A RAIN AND SNOW MIX AT ROA AND LYH THEN
CHANGE TO ALL SNOW AROUND 17Z AS THE STORM SYSTEM MOVES NORTHEAST AND
COLD AIR GETS PULLED INTO THE WEST SIDE OF THE LOW. THE CHANGE TO
SNOW AT DAN WILL BE LATER...AROUND 21Z. THE SNOW BE HEAVY ENOUGH
TO ACCUMULATE...THOUGH SHOULD BE SLUSHY AND WET. 

THE PRECIP WILL MOVE OUT OF THE AREA QUICKLY THIS EVENING FROM
SOUTHWEST TO NORTHEAST. CLOUDS WILL BECOME SCATTERED EAST OF THE
BLUE RIDGE AFTER 00Z WITH ROA...LYH AND DAN ALL VFR AFT 06Z. THE
CLEARING WILL BE SLOWER AT BLF AND LWB DUE TO AND WEST TO
NORTHWEST LOW LEVEL WIND AND RESIDUAL LOW LEVEL MOISTURE. 
ALL SITES SHOULD BECOME VFR BY 12Z SUNDAY. 

HIGH PRESSURE WILL CONTINUE THE VFR CONDITIONS INTO MONDAY.
A WEAK COLD FRONT MAY BRING BRIEF MVFR CONDITIONS IN CLOUDS AND
POSSIBLY LIGHT PRECIP BY MONDAY NIGHT INTO TUESDAY IN THE MOUNTAINS. IFR
CONDITIONS MAY BE POSSIBLE TUESDAY NIGHT AND WEDNESDAY WITH A
LARGER LOW PRESSURE SYSTEM DEVELOPING IN THE SOUTHERN PLAINS. 

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR VAZ007-
     009>018.
     WINTER STORM WARNING UNTIL 11 PM EST THIS EVENING FOR VAZ019-
     020-023-024.
     WINTER WEATHER ADVISORY FROM 10 AM THIS MORNING TO 11 PM EST 
     THIS EVENING FOR VAZ022-034-035-045>047.
NC...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR NCZ001-
     002-018.
WV...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR 
     WVZ042>045.

&&

$$
SYNOPSIS...RCS
NEAR TERM...RCS
SHORT TERM...AMS
LONG TERM...KK
AVIATION...AMS/PM